A flat-panel CRT display is a thin, flat display which presents an image on the display's viewing surface in response to electrons striking light-emissive material. The electrons can be generated by mechanisms such as field emission and thermionic emission. A flat-panel CRT display typically contains a faceplate (or frontplate) structure and a backplate (or baseplate) structure connected together through an annular outer wall. The resulting enclosure is held at a high vacuum. To prevent external forces such as air pressure from collapsing the display, one or more spacers are typically located between the plate structures inside the outer wall.
FIGS. 1 and 2, taken perpendicular to each other, schematically illustrate part of a conventional flat-panel CRT display such as that disclosed in Schmid et al, U.S. Pat. No. 5,675,212. The components of this conventional display include backplate structure 20, faceplate structure 22, and a group of spacers 24 situated between plate structures 20 and 22 for resisting external forces exerted on the display. Backplate structure 20 contains regions 26 that selectively emit electrons. Faceplate structure 22 contains elements 28 that emit light upon being struck by electrons emitted from electron-emissive regions 26. Each light-emissive element 28 is situated opposite a corresponding one of electron-emissive regions 26.
Each of spacers 24, one of which is fully labeled in FIGS. 1 and 2, consists of main spacer wall 30, end electrodes 32 and 34, a pair of face electrodes 36, and another pair of face electrodes 38. End electrodes 32 and 34 are situated on opposite ends of spacer wall 30 so as to contact plate structures 20 and 22. Face electrodes 36 form a continuous U-shaped electrode with end electrode 32. Face electrodes 38 form a continuous U-shaped electrode with end electrode 34.
It is desirable that spacers in a flat-panel CRT display not produce electrical effects which cause electrons to strike the display's faceplate structure at locations significantly different from where the electrons would strike the faceplate structure in the absence of the spacers. The net amount that the spacers cause electrons to be deflected sideways should be close to zero. Achieving this goal is especially challenging when, as occurs in the conventional display of FIGS. 1 and 2, the spacing between consecutive wall-shaped spacers is more than two electron-emissive regions. If spacers 24 cause net electron deflections, the net deflections of electrons emitted from regions 26 located different distances away from the nearest spacer 24 are typically different. This can lead to image degradation such as undesired features appearing on the display's viewing surface.
Face electrodes 36 and 38 are utilized to control the electric potential field along spacers 24 in order to reduce their net effect on the trajectories of electrons moving from regions 26 to elements 28. However, as discussed in Schmid et al, spacers 24 are typically made by a process in which large sheets of wall material having double-width strips of electrodes 36 and 38 formed on the sheets are mechanically cut along the centerlines of electrodes 36 and 38. Due to mechanical limitations in performing the cutting operation, the width of each face electrode 36 or 38 can vary along its length.
In turn, the variation in face-electrode width causes the electrical effect that spacers 24 have on the electron trajectories to vary along the spacer length. The net electron deflection resulting from spacers 24 thus varies along their length. Even if the net electron deflection is largely zero at one location along the spacer's length, the net electron deflection at other locations along the spacer's length can cause substantial image degradation. It is desirable to avoid image degradation that arises from width variations of face electrodes that contact end electrodes.